The present invention relates to an ABS (Antilock Brake System) apparatus for preventing wheels from being locked when quick braking is applied to a car.
A typical prior art ABS apparatus controls braking on a car wheel as follows. Specifically, the wheel is attached with a hub formed with gear teeth. When the gear teeth turn, the turning is detected by an electromagnetic pick up, and based on information detected by the electromagnetic pick up, a wheel speed is calculated. Next, a car speed is calculated from the wheel speed and signals from an acceleration sensor. Further, a slip rate is calculated from the wheel speed and the car speed, and this slip rate is used for controlling the braking on the wheel.
In such a system, it is very difficult to directly obtain the car speed, and therefore the car speed must be estimated from the wheel speed and the signals from the acceleration sensor. More specifically, it is impossible to obtain an accurate car speed, and as a result the control is inaccurate.
Further, when the car speed is slower, a pick-up cycle of the electromagnetic pick becomes accordingly longer, making the control more inaccurate. This problem is a serious shortcoming in the ABS apparatus since the ABS apparatus must keep performing from the time the car speed begins to decrease after a brake pedal is pressed to the time the car comes to a complete stop.
In order to solve the above problem, the inventor of the present invention proposed on ABS apparatus (Japanese Patent Laid-Open-9-2240) in which a differential parameter M according to a difference between road frictional force F and braking torque T is used in the control. Specifically, the ABS apparatus begins to reduce braking pressure when the differential parameter M decreases to a predetermined threshold while a brake is being applied.
However, the above ABS apparatus disclosed in the Japanese Patent Laid-Open 9-2240 does not make any proposal concerning control on a time for stopping the pressure reducing operation in the braking equipment. Further, no detailed proposal is made for control on varying the threshold for matching the timing for starting or stopping the pressure reducing operation concurrently with change in car speed and road conditions. Still further, no proposal is made for detecting or dealing with an over slip caused when the threshold value for starting or stopping the pressure reducing operation deviates from an ideal value.
It is therefore an object of the present invention to provide an ABS apparatus capable of controlling accurately regardless of change in the car speed or road conditions.
According to a first aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; and a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors. The ABS apparatus further comprises a brake fluid pressure controlling means for starting and then stopping a pressure reducing operation when the differential parameter M calculated by the differential parameter calculating means reaches a first threshold provided according to a peak value of the differential parameter M or a second threshold having an absolute value slightly smaller than that of the first threshold while the braking equipment is in operation.
According to a preferred embodiment of the present invention, the differential parameter calculating means obtains a value F-T as the differential parameter M by subtracting the braking torque T from the road frictional force F based on the braking torque information and road frictional force information from the first sensors.
According to another preferred embodiment of the present invention, the differential parameter calculating means obtains a value (R/r)F-T as the differential parameter M based on the braking torque information and road frictional force information from the first sensors; where R is a radius of the wheel, and r is a distance from a center of turning in the wheel to a braking calipers of the braking equipment. The differential parameter M is obtained by having a ratio of the radius R to the distance r multiplied by a value of the road frictional force F, and then subtracting a value of the braking torque T from the product.
According to another preferred embodiment of the present invention, the differential parameter M while the car is making a turn is obtained by using a cornering force Fs acting on the wheel vertically to a direction of car""s motion, instead of using the road frictional force F, from road frictional force information according to this cornering force Fs and braking torque information according to the braking torque T.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a steering angle sensor for detecting the steering angle of the wheel for calculating an angle of side slip xcex2 as a deviation between an axis vertical to an axis of tire rotation and the direction in which the car is moving, and the cornering force Fs is calculated from this angle of side slip xcex2.
According to a second aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors; and a brake fluid pressure controlling means for controlling brake fluid pressure of the braking equipment by using the differential parameter M and a first threshold according to a peak value of the differential parameter M. The ABS apparatus further comprises an arbitrary number of seconded sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car; and a gravitational acceleration change rate calculating means for calculating a gradient of locus given by the gravitational acceleration information from the second sensors. Road conditions are judged based on the gradient of the locus of gravitational acceleration information calculated by the gravitational acceleration change rate calculating means.
According to a preferred embodiment of the present invention, the brake fluid pressure controlling means starts and then stops a pressure reducing operation when the differential parameter M calculated by the differential parameter calculating means reaches a first threshold or a second threshold having an absolute value slightly smaller than that of the first threshold while the braking equipment is in operation.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a first threshold varying means for varying the first threshold according to the gradient of the locus of gravitational acceleration information calculated by the acceleration change rate calculating means.
According to a third aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors; and a brake fluid pressure controlling means for controlling brake fluid pressure of the braking equipment by using the differential parameter M and a first threshold according to a peak value of the differential parameter M. The ABS apparatus further comprises a road frictional force change rate calculating means for calculating a difference between a value of the road frictional force information at a time of a current start of a pressure reducing operation and a value of the road frictional force information at a time of a previous start of the pressure reducing operation; and a first threshold varying means for varying the first threshold according to an amount of change in the road frictional force information calculated by the road frictional force change rate calculating means.
According to a preferred embodiment of the present invention, the brake fluid pressure controlling means starts and then stops a pressure reducing operation when the differential parameter M calculated by the differential parameter calculating means reaches a first threshold or a second threshold having an absolute value slightly smaller than that of the first threshold while the braking equipment is in operation.
According to a fourth aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors; and a brake fluid pressure controlling means for controlling a brake fluid pressure by using the differential parameter M calculated by the differential parameter calculating means and a first threshold according to a peak value of the differential parameter M. The ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car, a wheel velocity parameter calculating means for calculating a wheel velocity parameter Mxcfx89 by integrating a difference between the differential parameter M calculated by the differential parameter calculating means and the gravitational acceleration information from the second sensor; a two point difference calculating means for calculating at a predetermined time interval a difference in the wheel velocity parameter Mxcfx89 calculated by the wheel velocity parameter calculating means; and a first threshold varying means for varying the first threshold according to the difference in the wheel velocity parameter Mxcfx89 calculated by the two point difference calculating means.
According to a preferred embodiment of the present invention, the brake fluid pressure controlling means starts and then stops a pressure reducing operation when the differential parameter M calculated by the differential parameter calculating means reaches the first threshold or a second threshold having an absolute value slightly smaller than that of the first threshold while the braking equipment is in operation.
According to a fifth aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors; and a brake fluid pressure controlling means for controlling a brake fluid pressure by using the differential parameter M calculated by the differential parameter calculating means and a first threshold according to a peak value of the differential parameter M. The ABS apparatus further comprises a wheel velocity parameter calculating means for calculating a wheel velocity parameter Mxcfx89 by integrating a difference between the differential parameter M calculated by the differential parameter calculating means and a value proportional to that of the first threshold; a two point difference calculating means for calculating at a predetermined time interval a difference in the wheel velocity parameter Mxcfx89 calculated by the wheel velocity parameter calculating means; and a first threshold varying means for varying the first threshold according to the difference in the wheel velocity parameter M xcfx89 calculated by the two point difference calculating means.
According to a preferred embodiment of the present invention, the brake fluid pressure controlling means starts and then stops a pressure reducing operation when the differential parameter M calculated by the differential parameter calculating means reaches a first threshold or a second threshold having an absolute value slightly smaller than that of the first threshold while the braking equipment is in operation.
According to a sixth aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining food frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors; and a brake fluid pressure controlling means for controlling brake fluid pressure of the braking equipment by using the differential parameter M and a first threshold according to a peak value of the differential parameter M. The ABS apparatus further comprises a differential parameter change rate calculating means for calculating a rate of change dM/dt in the differential parameter M calculated by the differential parameter calculating means; and an over-slip controlling means for judging an over slipping situation to be present in the wheel when the rate of change dM/dt calculated by the differential parameter change rate calculating means exceeds a third threshold and reducing a fluid pressure of the braking equipment while the braking equipment is in operation.
According to a preferred equipment of the present invention, the over-slip controlling means judges the over slipping situation to have been sufficiently eliminated and stops the pressure reducing operation of the braking equipment when a movement of the rate of change dM/dt calculated by the differential parameter change rate calculating means becomes smaller than a predetermined value after reducing the fluid pressure of the braking equipment.
According to another preferred embodiment of the present invention, the over-slip controlling means judges the over slipping situation to have been sufficiently eliminated and stops the pressure reducing operation of the braking equipment when a movement of the rate of change dM/dt calculated by the differential parameter change rate calculating means becomes smaller than a predetermined value continually for a plurality of times after reducing the fluid pressure of the braking equipment.
According to another preferred embodiment of the present invention, the over-slip controlling means judges the over slipping situation to have been sufficiently eliminated and stops the pressure reducing operation of the braking equipment if a value of M calculated by the differential parameter calculating means is greater than a predetermined value when a movement of the rate of change dM/dt calculated by the differential parameter change rate calculating means becomes smaller than a predetermined value after reducing the fluid pressure of the braking equipment.
According to another preferred embodiment of the present invention, the over-slip controlling means judges the over slipping situation to have been sufficiently eliminated and stops the pressure reducing operation of the breaking equipment if a value of M calculated by the differential parameter calculating means is greater than a predetermined value when a movement of the rate of change dM/dt calculated by the differential parameter change rate calculating means becomes smaller than a predetermined value continually for a plurality of times after reducing the fluid pressure of the braking equipment.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a first threshold varying means for varying the first threshold; and a first threshold resetting means for judging a friction coefficient to have decreased rapidly and setting the first threshold to a predetermined value if a value of the rate dM/dt calculated by the differential parameter change rate calculating means exceeds a fourth threshold having a sufficiently larger value than that of the third threshold while an over slipping situation is judged to be present by the over-slip controlling means.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a first threshold varying means for over slipping situation, for varying the first threshold according to a value of M calculated by the differential parameter calculating means when the over slipping situation of the wheel is judged to be present by the over-slip controlling means.
According to another preferred embodiment of the present invention, three absolute values are predetermined for the first threshold according to three respective levels of high xcexc, middle xcexc, and low xcexc according to the road friction coefficient. The first threshold varying means for over slipping situation replaces an absolute value of the first threshold with that of the low xcexc level if the differential parameter M calculated by the differential parameter calculating means has an absolute value not greater than a predetermined value having an absolute value slightly larger than that of the low xcexclevel, or replaces the absolute value of the first threshold with an average value of the current absolute value and that of the low xcexc level if the differential parameter M has an absolute value greater than a predetermined value having an absolute value slightly larger than that of the low xcexclevel but not greater than the absolute value for the middle xcexclevel, or replaces the absolute value of the first threshold with an average value of the current absolute value and that of the middle xcexc level if the differential parameter M has an absolute value greater than that of the middle xcexclevel, when the over slipping situation of the wheel is judged to be present by the over-slip controlling means.
According to a seventh aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment. The ABS apparatus further comprises differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors; a wheel velocity parameter calculating means for calculating a wheel velocity parameter Mxcfx89 which becomes 0 when the wheel is locked, by correcting and then integrating the differential parameter M calculated by the differential parameter calculating means; and a brake fluid pressure controlling means for controlling the fluid pressure of the braking equipment by using the wheel velocity parameter Mxcfx89 calculated by the wheel velocity parameter calculating means.
According to a preferred embodiment of the present invention, the ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car. The wheel velocity parameter calculating means obtains the wheel velocity parameter Mxcfx89 by integrating a difference between the differential parameter M and the gravitational acceleration G based on the gravitational acceleration information.
According to another preferred embodiment of the present invention, the wheel velocity parameter calculating means obtains the wheel velocity parameter Mxcfx89 by integrating a difference between the differential parameter M and a value proportional to the first threshold according to a peak value of the differential parameter M.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car; a gravitational acceleration change rate calculating means for calculating a gradient in a locus given by the gravitational acceleration G according to the gravitational acceleration information; and a first threshold varying means for varying the first threshold according to the gradient in the locus given by the gravitational acceleration G calculated by the gravitational acceleration change rate calculating means.
According to a preferred embodiment of the present invention, the ABS apparatus further comprises a two point difference calculating means for calculating a difference in the wheel velocity parameter Mxcfx89 at a predetermined time interval; and a first threshold varying means for varying the first threshold according to the difference in the wheel velocity parameter Mxcfx89 calculating by the two point difference calculating means.
According to a preferred embodiment of the present invention, the ABS apparatus further comprises a road frictional force change rate calculating means for calculating a difference between a value of the road frictional force information at a time of a current start of a pressure reducing operation and a value of the road frictional force information at a time of a previous start of the pressure reducing operation; and a first threshold varying means for varying the first threshold according to an amount of change in the road frictional force information calculated by the road frictional force change rate calculating means.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car; and a gravitational acceleration integrating means for integrating the gravitational acceleration G. The brake fluid pressure controlling means sets a reference line by translating the locus of the integration given by the gravitational acceleration integrating means so as to include a value of the wheel velocity parameter Mxcfx89 at a time when a brake fluid pressure reducing operation is started, and stops the brake fluid pressure reducing operation when the wheel velocity parameter Mxcfx89crosses the reference line after the brake fluid pressure reducing operation is started.
According to another preferred embodiment of the present invention, the brake fluid pressure controlling means sets a reference straight line passing a value of the wheel velocity parameter Mxcfx89 at a time when a brake fluid pressure reducing operation is started and a value of the wheel velocity parameter Mxcfx89 at a time retrospective by a predetermined amount of time to the time when the brake fluid pressure reducing operation is started, and stops the brake fluid pressure reducing operation when the wheel velocity parameter Mxcfx89crosses the reference line after the brake fluid pressure reducing operation is started.
According to another preferred embodiment of the present invention, the brake fluid pressure controlling means compares a gradient of the current reference line with that of a previous reference line, and corrects the current reference line by selecting a longer time interval than the predetermined time interval if there is an increase in the gradient, or by selecting a shorter time interval than the predetermined time interval if there is a decrease in the gradient.
According to another preferred embodiment of the present invention, the brake fluid pressure controlling means detects a time point when the differential parameter M has increased to a second threshold provided according to a peak value of the differential parameter M after starting a brake fluid pressure reducing operation, and stops the brake fluid pressure reducing operation if the above time point is after a predetermined minimum time period for the pressure reducing operation and if the brake fluid pressure reducing operation is not stopped yet.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car; and a gravitational acceleration integrating means for integrating the gravitational acceleration G according to the gravitational information. The brake fluid pressure controlling means sets a quick pressurization judging line by translating the locus of the integration given by the gravitational acceleration integrating means so as to include a value slightly larger than that of the wheel velocity parameter Mxcfx89 at a time when a brake fluid pressure reducing operation is started, for rapidly increasing the brake fluid pressure when the wheel velocity parameter Mxcfx89 crosses the quick pressurization judging line after the brake fluid pressure reducing operation is stopped.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car; and a gravitational acceleration integrating means for integrating the gravitational acceleration G according to the gravitational acceleration information. The brake fluid pressure controlling means judges an over slipping situation to be present in the wheel if a gradient of the locus given by the integration performed by the gravitational acceleration integrating means is smaller than a predetermined value when the wheel velocity parameter Wxcfx89 turns from decreasing to increasing.
According to another preferred embodiment of the present invention, the differential parameter calculating means obtains a value F-T by subtracting the braking torque T from the road frictional force F based on the braking torque information and road frictional force information from the first sensors as the differential parameter M.
According to another preferred embodiment of the present invention, the differential parameter calculating means obtains a value (R/r)F-T as the differential parameter M based on the braking torque information and road frictional force information from the first sensors; where R is a radius of the wheel, and r is a distance from a center of turning in the wheel to a braking calipers of the braking equipment. The differential parameter M is obtained by having a ratio of the radius R to the distance r multiplied by a value of the road frictional force F, and then subtracting a value of the braking torque T from the product.
According to another preferred embodiment of the present invention, the differential parameter M while the car is making a turn is obtained by using a cornering force Fs acting on the wheel vertically to a direction of car""s motion, instead of using the road frictional force F, from road frictional force information according to this cornering force Fs and braking torque information according to the braking torque T.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a steering angle sensor for detecting the steering angle of the wheel for calculating an angle of side slip xcex2 as a deviation between an axis vertical to an axis of tire rotation and the direction in which the car is moving, and the cornering force Fs is calculated from the angle of side slip xcex2.
According to an eighth aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment. The the ABS apparatus further comprises a differential parameter calculating means for calculating a differential parameter M according to a difference between the road frictional force information and the braking torque information from the first sensors; a wheel velocity parameter calculating means for calculating a wheel velocity parameter Mxcfx89 which becomes 0 when the wheel is locked, by correcting and then integrating the differential parameter M calculated by the differential parameter calculating means; a wheel velocity acceleration parameter calculating means for calculating a wheel velocity acceleration parameter dMxcfx89/dt by differentiating the wheel velocity parameter Mxcfx89 calculated by the wheel velocity parameter calculating means, and a brake fluid pressure controlling means for controlling the fluid pressue of the braking equipment by using the wheel acceleration parameter dM xcfx89 /dt calculated by the wheel acceleration parameter calculating means.
According to a preferred embodiment of the present invention, the ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car. The wheel velocity parameter calculating means obtains the wheel velocity parameter Mxcfx89 by integrating a difference between the differential parameter M and the gravitational acceleration G based on the gravitational acceleration information.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises an arbitrary number of second sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car; a gravitational acceleration change rate calculating means for calculating a gradient in a locus given by the gravitational acceleration G according to the gravitational acceleration information; and a first threshold varying means for varying the first threshold according to the gradient in the locus given by the gravitational acceleration G calculated by the gravitational acceleration change rate calculating means.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a two point difference calculating means for calculating a difference in the wheel velocity parameter Mxcfx89 at a predetermined time interval; and a first threshold varying means for varying the first threshold according to the difference in the wheel velocity parameter Mxcfx89 calculated by the two point difference calculating means.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a road frictional force change rate calculating means for calculating a difference between a value of the road frictional force F at a time of a current start of a pressure reducing operation and a value of the road frictional force F at a time of a previous start of the pressure reducing operation; and a first threshold varying means for varying the first threshold according to an amount of change in the road frictional force F calculated by the road frictional force change rate calculating means.
According to another preferred embodiment of the present invention, the brake fluid pressure controlling means stops the pressure reducing operation when wheel acceleration parameter dMxcfx89/dt reaches a second threshold after the brake fluid pressure reducing operation is started.
According to another preferred embodiment of the present invention, the brake fluid pressure controlling means rapidly increases the brake fluid pressure when the wheel acceleration parameter dMxcfx89/dt reaches a fifth threshold after the brake fluid pressure reducing operation is stopped.
According to another preferred embodiment of the present invention, the differential parameter calculating means obtains a value F-T as the differential parameter M by subtracting the braking torque T from the road frictional force F based on the braking torque information and road frictional force information from the first sensors.
According to another preferred embodiment of the present invention, the differential parameter calculating means obtains a value (R/r)F-T as the differential parameter M based on the braking torque information and road frictional force information from the first sensors; where R is a radius of the wheel, and r is a distance from a center of turning in the wheel to a braking calipers of the braking equipment. The differential parameter M is obtained by having a ratio of the radius R to the distance r multiplied by a value of the road frictional force F, and then subtracting a value of the braking torque T from the product.
According to another preferred embodiment of the present invention, the differential parameter M while the car is making a turn is obtained by using a cornering force Fs acting on the wheel vertically to a direction of car""s motion, instead of using the road frictional force F, from road frictional force information according to this cornering force Fs and braking torque information according to the braking torque T.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a steering angle sensor for detecting the steering angle of the wheel for calculating an angle of side slip xcex2 as a deviation between an axis vertical to an axis of tire rotation and the direction in which the car is moving, and the cornering force Fs is calculated from the angle of side slip xcex2.
Other various features and advantages of the present invention will become clear from description given below with reference to the accompanying drawings.